textproduct: Rapid City

KEY MESSAGES

- Chances for isolated storms/showers daily.

- Chance for a couple severe storms this afternoon across southwest and south central SD.

- Warming up for the weekend.

UPDATE

Issued at 930 PM MDT Wed Aug 26 2026

Pos theta-e adv can be expected tonight across the western SD Plains. This may support elevated isolated shra/TS there through morning as a weak impulse traverses NW flow aloft. Deep layer moisture will spread into the region Thur per SE ll flow. This will support 1500-2000 J/kg of MLCAPE by afternoon. Weak CIN coupled with a passing impulse will support TS chances by afternoon, esp across scentral SD and SW SD. Deep layer shear of 40 to 50 knots will support the potential for supercells as storms progress SE. Have adjusted pops for this. Otherwise, isold shra/ts will be possible Thur night across the NW, with low chances continuing through much of the weekend.

DISCUSSION

(This Evening Through Wednesday) Issued at 114 PM MDT Wed Aug 26 2026

Current upper air models show ridge over the Rockies, with northwest flow over the forecast area. 19Z surface analysis shows high pressure over western North Dakota this afternoon, while a frontal boundary sits over eastern Wyoming into Nebraska. Winds are currently light and variable over the area, with temperatures in the 80s. Satellite shows some CU development over the Black Hills, otherwise mostly clear skies.

An isolated strong to severe storm cannot be ruled out this afternoon and evening. The best chance for storms will be in the Black Hills, as well as northeast Wyoming to southwest SD closer to the frontal boundary. CAPE values in the 200-500 j/Kg range along with eff shear 30-40kts and modest lapse rates will support a small hail and wind threat if any storms are able to get going. Another weak disturbance progged to move through the region Thursday, bringing more isolated storm chances, mainly over the Black Hills to southwestern SD. Later Thursday into Friday the upper ridge moves over the region, prompting warmer temperatures, with highs over the weekend ranging from the upper 80s to near 100. Sunday into Monday an upper low treks across the northern plains and southern Canada, however better forcing looks to remain north of our area. Cannot rule out some showers and storms on Sunday, mainly over northwestern SD.

As the upper low slides eastward, pattern shifts for our region, with southwest flow setting up early next week. This will lower temperatures a bit before shortwave ridging moves back in Tuesday. In typical August fashion, weak disturbances will bring near daily chances for isolated showers and storms.

AVIATION

(For the 12Z TAFS Through 12Z Friday Morning) Issued At 526 AM MDT Thu Aug 27 2026

Can't completely rule out an isolated shower or thunderstorm this morning north of I-90 in South Dakota as a weak impulse moves through, but more impactful chances will be this afternoon, albeit still leaning isolated in coverage. CAMs favor the corridor from the Black Hills down across the plains along and south of I-90, with initiation as early as 18-19z/12-1pm with everything ending along the Nebraska border by about 02z/8pm. Consensus on timing and location isn't great, but the risk is enough to introduce a several hour PROB30 for KRAP. Shear values may support a couple supercells, so the strongest storms today will be capable of producing large hail, gusty/erratic winds in excess of 40kts, and vsby drops to MVFR or even IFR under cores. This said, large swaths of the region outside any isolated storms will remain solidly VFR. We may also see some gusty shower activity try to come in from the west across northeastern Wyoming this evening, but confidence is currently low on that scenario. Expect breezy south winds tonight at KGCC.

UNR WATCHES/WARNINGS/ADVISORIES

SD...None. WY...None.